Speed control circuit for a dc brushless motor

ABSTRACT

The speed control circuit in accordance with the present invention mainly includes a switch circuit and a voltage-detection circuit. The voltage-detection circuit is actuated depending upon high or low voltage of power supply to thereby determine the switch circuit to output high or low operating voltage to a driver circuit of the motor in response to changes of the voltage of the power supply. The motor is adjusted and operated at desired speeds by a rated range of input voltage according to the high or low operating voltage.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention is related to a speed control circuit for a dc brushless motor and more particularly to a switch circuit and a voltage-detection circuit changing motor speed in various speed features of the dc brushless motor in response to changes of voltage of power supply.

[0003] 2. Description of the Related Art

[0004] Currently, fans are used for forced air cooling of the electronic devices, such as power supply, CPU of computers, display card, and computer components etc. Recently, there is a trend to adjustably operate fans at high or low speed depending upon ambient conditions. In high temperature ambiance, a fan must operate at high speed to reduce or remove heats produced by electronic components so as to ensure these electronic components being operated in normal and avoid these heats resulting in damage to these electronic components. In low temperature ambiance, the fan must operate at low adequate speed for saving power and decreasing noise.

[0005]FIG. 1 illustrates a schematic view of a traditional driver circuit for a single phase dc brushless motor.

[0006] Referring to FIG. 1, the driver circuit for the single phase dc brushless motor includes a coil L1, a Hall element IC1, a driver element IC2, and a capacitor C1. The Hall element IC1 is used for detecting changes of a permanent magnetic field of a rotor to thereby output weaker Hall voltage. And then the Hall voltage is magnified by the driver circuit IC2 to further output alternative signals (square waveforms) from two terminals O1 and O2 to the bridging transistors Q1 through Q4. The coil L1 is actuated in turn to change current in direction so as to rotate the rotor. FIG. 2 illustrates a schematic view of a traditional driver circuit for a double phase dc brushless motor.

[0007] Referring to FIG. 1, the driver circuit for the double phase dc brushless motor includes a first coil L1, a second coil L2, a capacitor C1, a Hall driver element IC3, a first resistor R1, a second resistor R2, and a transistor Q1. The resistors R1 and R2 and transistor Q1 are consisted of a rotational speed detective circuit. The Hall driver element IC3 is used for detecting changes of a permanent magnetic field of a rotor and then the Hall voltage is magnified to output alternative signals (square waveforms) from two terminals O1 and O2 to the coils L1 and L2 respectively. The coils L1 and L2 are actuated in turn to change current so as to rotate the rotor.

[0008] In cooling fan system, there is generally providing two voltage levels to a driver circuit for various desired amounts of forced air. For example, a high voltage level 12V controls a fan operating at 3000 rpm, and a low voltage level 6V at 1500 rpm. Therefore, the cooling fan system operates at different speeds to provide cooling capacity depending upon the ambient conditions.

[0009]FIG. 3 illustrates a voltage diagram for speed of a traditional dc brushless motor. Between two specific voltages, ranged from 12V to 6V for example, have high speed, low speed and nonlinear feature. When the cooling fan system is input 12V, the motor is operated at high speed 3000 rpm; if when the cooling fan system is changed to input 6V, the motor is operated at low speed 2000 rpm according to the nonlinear feature. Accordingly, the cooling fan system fails to certainly operate at predetermined low speed 1500 rpm and to meet the system demand.

[0010] The motor structure and the nonlinear feature limit the traditional dc brushless motor whose speed cannot be adjusted depending upon the system needs. In order to improve these limitations of the traditional motor to perform desired speeds, it is necessary to be redesigned.

[0011] The present invention intends to provide a speed control circuit comprising a switch circuit and a voltage-detection circuit used for adjusting an operating voltage depending upon speeds of the motor. The operating voltage of desired speed of the motor is determined by the rated range of input voltage in such a way to mitigate and overcome the above problem.

SUMMARY OF THE INVENTION

[0012] The primary objective of this invention is to provide a speed control circuit for a dc brushless motor comprising a switch circuit and a voltage-detection circuit used for adjusting operating voltage depending upon speeds of the motor.

[0013] The secondary objective of this invention is to provide a speed control circuit for a dc brushless motor using a switch circuit to determine an operating voltage of low speed.

[0014] The present invention is a speed control circuit for a dc brushless motor. The speed control circuit includes a switch circuit and a voltage-detection circuit. The voltage-detection circuit is actuated depending upon high or low voltage of power supply to thereby determine the switch circuit to output high or low operating voltage to a driver circuit of the motor in response to changes of the voltage of the power supply. The motor is adjusted and operated at desired speeds by a rated range of input voltage according to the high or low operating voltage.

[0015] Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will now be described in details with references to the accompanying drawings herein:

[0017]FIG. 1 is a schematic view of a traditional driver circuit for a single phase dc brushless motor;

[0018]FIG. 2 is a schematic view of a traditional driver circuit for a double phase dc brushless motor;

[0019]FIG. 3 is a voltage diagram for speed of a traditional dc brushless motor;

[0020]FIG. 4 is a block diagram of a speed control circuit for a dc brushless motor in accordance with the present invention;

[0021]FIG. 5 is a voltage diagram for speed of a speed control circuit in accordance with the present invention;

[0022]FIG. 6 is a schematic view of a speed control circuit in accordance with a first embodiment of the present invention applied in a driver circuit for a single phase dc brushless motor; and

[0023]FIG. 7 is a schematic view of a speed control circuit in accordance with a second embodiment of the present invention applied in a driver circuit for a double phase dc brushless motor.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Referring now to the drawings, there are two embodiments of the present invention shown therein, which include generally a driver member and a speed control member.

[0025]FIG. 4 illustrates a block diagram of a speed control circuit for a dc brushless motor in accordance with the present invention.

[0026] Referring initially to FIG. 4, the speed control circuit 10 includes a switch circuit 11 comprising an adjusting resistor and a voltage-detection circuit 12. The switch circuit 11 is adapted to control power supply to output a high or low operating voltage to a driver circuit 1 of the motor. And the voltage-detection circuit 12 is adapted depending upon high or low voltage of the power supply to actuate the switch circuit 11 in response to changes of the voltages of the power supply.

[0027]FIG. 5 illustrates a voltage diagram for speed of a speed control circuit in accordance with the present invention. Referring to FIGS. 4 and 5, when the system is input high voltage 12V, the switch circuit 11 is actuated to be closed by the voltage-detection circuit 12 and thus the motor can be input a high operating voltage 12V from the switch circuit 11. The motor is capable of operating and maintaining at high speed 3000 rpm until the input operating voltage is changed to a low voltage. When the system is changed to be input a low voltage 6V, the switch circuit 11 is actuated to be opened by the voltage-detection circuit 12 and thus the motor can be input a predetermined low operating voltage xV dropped by the adjusting resistor. The motor is capable of operating and maintaining at low speed 1500 rpm.

[0028]FIG. 6 illustrates a speed control circuit in accordance with a first embodiment of the present invention applied in a driver circuit for a single phase dc brushless motor. Referring to FIGS. 1 and 6, reference numerals of the first embodiment have applied the identical numerals of the traditional single phase dc brushless motor. The driver circuit of the first embodiment has the similar configuration and same function as the traditional driver circuit and the detailed descriptions are omitted.

[0029] Referring now to FIG. 6, the speed control circuit 10 in accordance with the first embodiment of the present invention is connected to the driver circuit 1 of the single phase dc brushless motor. The speed control circuit 10 includes a switch circuit 11 consisted of a transistor Q2, a resistor R3, and a resistor R4. The resistor R4 is an adjusting resistor Rx. When the transistor Q2 is cut off, the voltage of the power supply Vcc is passed the resistor R4 and dropped. And then this voltage drop is output to the driver circuit 1 of the motor.

[0030] Referring again to FIG. 6, the speed control circuit 10 further includes a voltage-detection circuit 12 consisted of a transistor Q3, a resistor R5, and a resistor R6. When the transistor Q3 is saturated, a current from the power supply Vcc can pass a base of the transistor Q2 and the resistor R3 to form a bias current between a collector and an emitter of the transistor Q3. Consequently, the transistor Q2 is saturated, and the power supply Vcc is output to the driver circuit 1 through an emitter and a collector of the transistor Q2 so as to output a high operating voltage. This high operating voltage is input into the driver circuit 1 and thus the motor (coil L1) is operated at high speed, as shown in FIG. 5. When the transistor Q3 is cut off, the voltage of the collector of the transistor Q3 is risen that cuts off a bias current between an emitter and a base of the transistor Q2. Consequently, the transistor Q2 (bias current) is cut off, and the power supply Vcc is input into the resistor R4 and dropped so as to output a low operating voltage. This low operating voltage is input into the driver circuit 1 and thus the motor (coil L1) is operated at low speed, as shown in FIG. 5. The resistors R5 and R6 consisted in a voltage divider. The voltage divider divides the voltage of the power supply Vcc to output a high voltage level (0.6-0.7V) to saturate the transistor Q3 when the power supply is risen above a reference voltage (xV). The transistor Q2 is actuated to saturate by means of switching to saturate the transistor Q3. By contrast, the voltage divider outputs a low voltage level to cut off the transistor Q3 when the power supply is fallen below the reference voltage. Similarly, the transistor Q2 is actuated to cut off by means of switching to cut off the transistor Q3.

[0031]FIG. 7 illustrates a speed control circuit in accordance with a second embodiment of the present invention applied in a driver circuit for a double phase dc brushless motor. Referring to FIGS. 2 and 7, reference numerals of the second embodiment have applied the identical numerals of the traditional double phase dc brushless motor. The driver circuit of the second embodiment has the similar configuration and same function as the traditional driver circuit and the detailed descriptions are omitted.

[0032] Referring now to FIG. 7, the speed control circuit 10 in accordance with the second embodiment of the present invention is connected to the driver circuit 1 of the double phase dc brushless motor. The speed control circuit 10 includes a switch circuit 11 consisted of a transistor Q2, and a resistor R4. The resistor R4 is an adjusting resistor Rx. When the transistor Q2 is cut off, the Hall driver circuit IC3 is dropped by the resistor R4 and then grounded. Thus the motor is operated at low speed, as shown in FIG. 5. When the transistor Q2 is saturated, the Hall driver circuit IC3 is grounded through a collector and an emitter of the transistor Q2. Thus the motor is operated at high speed, as shown in FIG. 5.

[0033] Referring again to FIG. 7, the speed control circuit 10 further includes a voltage-detection circuit 12 consisted of a resistor R5, and a resistor R6. The resistors R5 and R6 consisted in a voltage divider. The voltage divider divides the voltage of the power supply Vcc to output a high voltage level (0.6-0.7V) to saturate the transistor Q2 when the power supply is risen above a reference voltage (xV). Consequently, the Hall driver circuit IC3 is grounded through the transistor Q2 and the coils L1 and L2 are operated at the high operating voltage. By contrast, the voltage divider outputs a low voltage level to cut off the transistor Q2 when the power supply is fallen below the reference voltage. Consequently, the Hall driver circuit IC3 is grounded through the resistor R4 and the coils L1 and L2 are operated at the low operating voltage.

[0034] Although the invention has been described in details with references to its presently preferred embodiment, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the invention, as set forth in the appended claims. 

What is claimed is:
 1. A speed control circuit for a dc brushless motor comprising: a switch circuit being adapted to output a high or low operating voltage to a driver circuit of the motor from a power supply; and a voltage-detection circuit being adapted to control the switch circuit to switch outputting the high or low operating voltage in response to changes of a voltage of the power supply; wherein when the voltage-detection circuit senses a high voltage of the power supply, the switch circuit is actuated to output the high operating voltage to the driver circuit and thus the motor is operated at a high speed; and wherein when the voltage-detection circuit senses a low voltage of the power supply, the switch circuit is actuated to output the low operating voltage to the driver circuit and thus the motor is operated at a low speed.
 2. The speed control circuit for a dc brushless motor as defined in claim 1, wherein the speed control circuit is applied to a single phase dc brushless motor.
 3. The speed control circuit for a dc brushless motor as defined in claim 2, wherein the switch circuit is consisted of a transistor Q2, a resistor R3, and a resistor R4 (Rx); the voltage-detection circuit is consisted of a transistor Q3, a resistor R5, and a resistor R6; when the transistor Q3 is saturated resulting in saturation of the transistor Q2, the power supply Vcc is output to the driver circuit through the transistor Q2 so as to output the high operating voltage to the driver circuit and thus the motor is operated at the high speed; when the transistor Q3 is cut off resulting in cutting off the transistor Q2, the power supply Vcc is dropped by the resistor R4 so as to output the low operating voltage to the driver circuit and thus the motor is operated at the low speed.
 4. The speed control circuit for a dc brushless motor as defined in claim 3, wherein the resistors R5 and R6 consisted in a voltage divider; when the power supply is risen above a reference voltage, the voltage divider divides the voltage of the power supply Vcc to output the high voltage level to saturate the transistor Q3 and subsequently saturate the transistor Q2; when the power supply is fallen below the reference voltage, the voltage divider outputs the low voltage level to cut off the transistor Q3 and subsequently cut off the transistor Q2.
 5. The speed control circuit for a dc brushless motor as defined in claim 1, wherein the speed control circuit is applied to a double phase dc brushless motor.
 6. The speed control circuit for a dc brushless motor as defined in claim 5, wherein the switch circuit is consisted of a transistor Q2, and a resistor R4 (Rx); the voltage-detection circuit is consisted of a resistor R5, and a resistor R6; when the transistor Q2 is cut off, a Hall driver circuit IC3 is dropped by the resistor R4 to ground and the motor is operated at the low speed; when the transistor Q2 is saturated, the Hall driver circuit IC3 is grounded through the transistor Q2 and thus the motor is operated at the high speed.
 7. The speed control circuit for a dc brushless motor as defined in claim 6, wherein the resistors R5 and R6 is consisted in a voltage divider; when the power supply is risen above a reference voltage, the voltage divider divides the voltage of the power supply Vcc to output a high voltage level to saturate the transistor Q2 and consequently the Hall driver circuit IC3 is grounded; when the power supply is fallen below the reference voltage, the transistor Q2 is cut off and consequently the Hall driver circuit IC3 is grounded through the resistor R4.
 8. The speed control circuit for a dc brushless motor as defined in claim 1, wherein the speed control circuit further comprises an adjusting resistor (Rx) to thereby drop the low voltage of the power supply that can output a predetermined low operating voltage to the driver circuit of the motor. 